Antistatic support

ABSTRACT

The antistatic desk pad for a working station in the electronic field is comprised of a rubber sheet with a resistance of at least 10 2  Ω cm. The upper portion of the sheet is provided with cavities of which the length is at least 8 mm, those cavities being intended to receive the debris of wires or the like.

The present invention relates to an antistatic support for work placesserving for the manipulation of electronic components and composed of arubber layer having a specific volume resistance (according to DIN53482) of at least 10² Ωcm.

The damage to electronic components by the effects of electrostaticcharges constitutes a problem which increases with the sensitivity ofsuch components. Of particular significance is the high capacitanceconstituted by a human being. Values up to 4,000 pF have already beenmeasured and the mean value is in the order of about 200 pF. Due torubbing against articles of clothing, the floor, seating surfaces andthe like the body is electrostatically charged up to peak voltages of6,000 volts. The discharge of such voltages across an electroniccomponent can lead to its destruction, and the damage need not beimmediately noticeable, rather can be present in terms of appreciablyimpairing the service life.

Particularly endangered electronic components are, for instance,so-called CMOS switching circuits, because their insulated controlelectrode (gate) possesses a high impedance and capacitively influencesthe flow of current. Such type of switching circuits possess anextremely thin dielectric film which is suitable for taking-up anundesired charging state, whereby then, if there is exceeded a criticalthreshhold, there occurs a breakdown through the dielectric to groundpotential. Also a great many other electronic components are highlysensitive to antistatic charges.

In order to counteract such problem there are used simultaneously at thepresent time three measures:

1. The work rooms are furnished with ionized air, so that in this waythere can be accomplished a neutralization of electrical charges,

2. The relevant operator is grounded by means of a conductive bandthrough a protective resistance, and finally there is ensured

3. That all work is accomplished at supports which ensure for a rapidremoval of electrostatic charges.

As an additional safety factor there are also used floor covering matswhich cause grounding of all persons who come into the vicinity of thework place.

The known antistatic supports possess a multi-layer construction, andthe top layer consists of a mass of ground conductive plastic material.Located therebelow is a highly conductive intermediate layer, forinstance in the form of a mesh composed of carbon fibers. Below suchthere is finally located a foamed plastic layer for increased comfortand an underside composed of a material resistent to sliding.

This known support can attain the desired effect of removing antistaticcharges, but it is however relatively uneconomical by virtue of itscomplicated construction. Additionally, the temperature resistance ofthe plastic material used in the top layer is not sufficient in order toavoid damage to such layer, for instance during unintentional contactwith a soldering iron. In fact, there exists the danger that uponburning through the top layer the highly conductive intermediate layerwill be exposed, which can lead not only to undesired short-circuits ofthe manipulated components, but even constitutes a certain danger in theevent there come into contact therewith bare conductor parts.

There have also already become known supports formed of antistaticrubber material. These supports likewise possess, just as was the casefor the above-mentioned multi-layer supports, an essentially smooth, ifdesired, slightly structured top surface. During the course of the workwhich is performed at such type of support, for instance the fabricationof electronic circuits, such support becomes contaminated by wirepieces, solder material and waste, and hence, hinders a rapid and cleanwork.

Therefore, the present invention has for its object the provision of anantistatic support which from the standpoint of electrical safety is100% satisfactory, affords a positive withdrawal of electrical chargesfrom antistatically charged bodies, is resistant against sliding, andalways presents a clean work surface even over longer periods of use.

This is achieved according to the invention with an antistatic supportof the previously mentioned type in that, at least a part of the topsurface of the support possesses preferably uniformly distributedrecesses, the extent or dimension of which, in plan view, as measured inat least one direction amounts to at least 8 mm, preferably at least 10mm.

This construction of an antistatic support satisfies in all aspects theabove explained objectives. In particular, it is thus possible toachieve the result that wire pieces and the like drop into the recessesand no longer are disturbingly present at the actual work surface. Dueto this construction of the surface of the antistatic support there isobtained, by virtue of the surface structuring by means of the recesses,a good contact possibility to parts placed thereon. Electroniccomponents are frequently also packaged in conductive bags whichlikewise during the transport electrostatically charge upon the worksurface. Therefore, measures must be taken to ensure that such charge iswithdrawn upon deposition of the bags upon the support. This can beparticularly rapidly accomplished with a support according to theinvention, since the transfer resistance, for instance from the supportto the bags, is maintained small.

Of course, the antistatic support is grounded, since otherwise therecould not be accomplished an outflow of the charges. Frequently there isprovided at the wall bounding the workplace or at the floor a groundingrail at which there can be electrically conductively connected thesupports at the work place and, if desired, at the floor. To ensure thatthe operating personnel itself likewise possesses as small as possiblecharge, there are used conductive hand bands which are conductivelyconnected by means of a suitable connection, for instance a push buttonor a Dutch tong with the support located at the work place.

Regarding the dimensions of the inventive recesses, it is necessary tostart with the fact that the wire pieces which are produced as wasteduring the work possess a maximum length of about 8 mm., so that in anyevent they have place within the recess. The recesses should bedistributed at least over the part of the top surface which is used forperforming the work, and the spaces between the recesses should not betoo great.

An appreciable safety advantage of the inventive antistatic supportformed of rubber can be realized in that, in contrast to the knownplastic supports, it is also equipped to be outstandingly protectedagainst fires. By the addition of suitable fire protection agents to therubber and the selection of suitable rubber compositions it is possibleto extensively minimize the danger of fires. It is therefore possible toeliminate the danger of fires owing to negligent handling of thesoldering iron.

Advantageously, the depth of the recesses can amount to 2 to 5 mm,preferably 3 to 4 mm. This depth of the recesses ensures that thewaste-wire pieces will come to lie within the recesses, and even aninclined position of such wire pieces still will not cause anyprotruding out thereof from the recesses and thus into the workingregion. What is also advantageous with such dimensioning of the recessesis that the recesses can be used during the work for fixing certaincomponents, so that there can be effectively prevented any unintentionalbrushing away thereof due to movements of the hand of the operator.

In order to avoid that the aforementioned wire pieces come to lie at thewebs between the recesses, it is advantageous if the web width of thematerial between the recesses amounts to 1 to 5 mm. Due to the averagelength of the wire pieces, as a general rule, there results a tilting ofsuch wire pieces into the recesses, so that the desired effect ofmaintaining free the actual work surface from contaminants can beobtained.

There is also then favored the above-discussed dropping-in of the wirepieces if the recesses widen outwardly in a trough-like fashion.Consequently, the walls of the recesses are somewhat inclined and renderpossible a rolling and sliding action. This construction is alsoadvantageous for the cleaning of the support, since as a result thereare not formed any corners and angles from which contaminants would bedifficult to remove.

An embodiment of the invention contemplates that the recesses, in planview, are constructed to be parallelogram-like in configuration. Themajor axis of the parallelogram can then be oriented approximatelyparallel to the work place edge which confronts the operator, so that asa general rule the wire pieces can drop in this direction of therecesses. The parallelograms are arranged with their shorter axes awayfrom the operator, so that there is formed a somewhat compacter surfacein this direction.

A further advantageous construction of the invention contemplates thatthe recesses, in plan view, possess a preferably triangular rondularprofile. Rondular profiles are characterized by the fact that theirchords leading to the center, just as is the case for circles withregard to their diameter, all have the same length. Thus, it is of noimportance in the case of a rondular cross-section in which directionthe wire pieces drop down: in any event they drop in the correctorientation into the recess.

As already above-discussed the antistatic support is connected, ifdesired, by means of Dutch tongs with a grounding rail. An advantageousmounting of the Dutch tong is then possible if the support possesses athickened portion at least at one side along the edge. The Dutch tongthen can be clamped over this thickened portion. However, the thickenedportion also acts as a barrier against the dropping-off of componentsfrom the support, which likewise constitutes a desired effect. Ananalogous effect is also then realizable if the support possesses agroove at least at one side along the edge. This groove likewise servesfor catching components which otherwise could be wiped-off of thesupport.

In many instances it is advantageous if the support only possessesrecesses at its top surface, whereas the bottom surface is essentiallysmooth and, at most, possesses a design which improves its resistance tosliding. In the case of such type of construction of a support, it ispossible, when performing working manipulations where suchcharacteristic is possibly desirable, to reverse the support, so thatits essentially smooth lower surface becomes the top surface.

In order to render possible use of the support at both sides in thesense of the present invention it is however advantageous if the topsurface and bottom surface of the support possess recesses.

According to an advantageous construction of an antistatic supportaccording to the present invention such possesses a surface resistance,measured in accordance with DIN 53596, of at most 10 Ωcm. Due to thisresistance characteristic there is ensured that there prevails over theentire surface of the support always an essentially equal potential,which also holds true for the electronic components which are depositedat different locations of the antistatic support.

In the description to follow there will be more fully explained by wayof example the invention based upon the drawings.

FIG. 1 illustrates a top plan view of a support,

FIG. 2 a fragmentary view of a top plan view, and

FIGS. 3 and 4 are cross-sectional views through partial regions.

In FIG. 1 there is illustrated a support 1 which in plan viewessentially possesses square recesses 2. Along the edge the support 1possesses a thickened portion 5 over which there can be placed at asuitable location a Dutch tong 8 which brings about the conductiveconnection to a ground conductor.

The recesses of the support 1 can possess in plan view any other desiredgeometric shape. In FIG. 2 there is illustrated a section of a support1, and the recesses 3 possess in plan view the shape of a tri-rondularconfiguration. As above-explained due to this construction there isattained the result that it is immaterial in which direction droppingwire pieces fall into the recesses, since such possesses the samediameter in all directions.

FIG. 3 illustrates a partial region of a support 1 in cross-section.There will be recognized that the recesses 4 are separated by webs 6.The walls of the webs 6 drop in a concave curved fashion towards thebase of the recess 4, so that there is favored a sliding-in of wirepieces. The inclining of the walls of the web 6 can also be flatter andis dependent upon the special requirements of the relevant work place.

In FIG. 4 there is shown a portion of a marginal region, incross-section, of a support 1. There will be recognized the thickenededge portion 5 which in cross-section is approximately eliptical. At theunderside of the support 1 there is located, adjacent the thickenedportion 5, an encircling groove 7 which then has ascribed theretoincreased significance if the support 1 is used in a reversed position.The thickened portion 5, among other things, serves for the connectionof a Dutch tong for the ground conductor and for the conductive armband.

What we claim is:
 1. An antistatic grounded support for work placesserving for the manipulation of electronic components, said antistaticsupport comprising:a rubber layer having a specific volume resistance(according to DIN 53482) of at least 10² Ωcm, a sufficiently low surfaceresistance for conducting away any static charges which may accumulatethereon, and defining two surfaces; at least a portion of one of saidtwo surfaces of said rubber layer is provided with recesses having abottom and serving for the reception of waste materials; said one ofsaid two surfaces of the rubber layer constituting the top surfacethereof which is used for performing work thereupon; and each saidrecess having, in top plan view, a dimension of at least 8 mm in atleast one direction; said recesses each have a depth in the range of 2to 5 mm; webs formed between said recesses; and each said web having awidth of material between the recesses in the range of 1 to 5 mm.
 2. Theantistatic support as defined in claim 1, wherein:each said recesswidens in a trough-like fashion from said bottom towards the outside. 3.The antistatic support as defined in claim 1, wherein:each said recess,in top plan view, possesses a parallelogram-like configuration.
 4. Theantistatic support as defined in claim 1, wherein:each said recess, intop plan view, possesses a tri-rondular configuration.
 5. The antistaticsupport as defined in claim 1, further including:a thickened portionformed at least at one side along an edge of said rubber layer.
 6. Theantistatic support as defined in claim 1, further including:a grooveformed at least at one side along an edge of said rubber layer.
 7. Theantistatic support as defined in claim 1, wherein:both said two surfacesof said rubber layer possess recesses.
 8. The antistatic support asdefined in claim 1, wherein:said rubber layer possesses a maximumsurface resistance, measured according to DIN 53496, of 10Ω.
 9. Theantistatic support as defined in claim 1, wherein:said recesses areessentially uniformly distributed at said portion of said one surface ofsaid rubber layer.
 10. The antistatic support as defined in claim 1,wherein:said recesses having a dimension of at least 10 mm in said atleast one direction.
 11. The antistatic support as defined in claim 2,wherein:said recesses have a depth in the range of 3 to 4 mm.